Thermal Hydraulic Considerations in Steady State Design

Transcription

1 Thermal Hydraulic Considerations in Steady State Design 1. PWR Design 2. BWR Design Course 22.39, Lecture 18 11/10/05 1

2 PWR Design Unless specified otherwise, all figures in this presentation are from: Shuffler, C., J. Trant, N. Todreas, and A. Romano. "Application of Hydride Fuels to Enhance Pressurized Water Reactor Performance." MIT-NFC-TR-077. Cambridge, MA: MIT CANES, January Courtesy of MIT CANES. Used with permission. 2

3 Components of Margin for MDNBR Overpower Transient 3800 MW th 4456 MW th 3

4 Summary of Steady-State Thermal Hydraulic Design Constraints 4

5 MDNBR vs Power Source: Blair, S., and N.E. Todreas. "Thermal Hydraulic Performance Analysis of a Small Integral Pressurized Water Reactor Core." MIT-ANP-TR-099. Cambridge MA: MIT CANES, December Courtesy of MIT CANES. Used with permission. 5

6 Flow-Induced Vibration Mechanisms 6

7 Vibrations Analysis Assumptions The fuel rod is modeled as a linear structure Changes to the fuel assembly structure over time are not considered Only the cladding structure is considered in the fuel rod model Only the first vibration mode is considered Core power is the only operating parameter affecting the vibrations performance of new designs 7

8 Summary of Steady-State Thermal Hydraulic Design Constraints 8

9 9 Vortex Shedding The vortex shedding margins in the lift and drag directions are defined as: VSM lift = f 1 f f s s (3.18) VSM drag = The vortex shedding frequency is given by: f 1 2 f s 2 f s where, f 1 : fundamental frequency of the rod (3.19) Vcross f = S (3.15) s D where the Strouhal number, S, was found by Weaver and Fitzpatrick to depend on the P/D ratio and channel shape. For square arrays, 1 (3.16) S = 2 ( P D 1) and for hexagonal arrays, S = 1 (3.17) 1.73(P D 1)

10 Fluid Elastic Instability The ratio of the maximum effective cross-flow velocity in the hot assembly, V eff, to the critical velocity for the bundle geometry V critical : FIM = V V eff (3.21) critical The most widely accepted correlation for estimating the critical velocity for a tube bundle is Connor s equation: V critical = β f n 2 π ζ m t ρ fl (3.23) where Pettigrew suggested a P/D effect on Connors constant: β=4.76 P D (3.24) The critical velocity is constant for a fixed geometry and, with the exception of small changes in coolant density, does not depend on the power and flow conditions in the core. 10

11 11 W Fretting Wear ( 3 2 f fretting,new 1 m t y ) rms new T c,ref 3 2 W ( fretting,ref f 1 m t y ) rms Tc,new ref = (3.39) where y rms is turbulence induced vibration from axial and cross flow, m t is total linear mass, and f 1 is fundamental frequency of fuel rod. The wear rate ratio is the constrained parameter, and the ratio of the cycle lengths is the design limit. If a new design has a shorter cycle length than the reference core, then it can safely accommodate a higher rate of wear. The wear rate limit, due to its dependence on cycle length, will depend on both the power and the fuel burnup. The power, however, depends on the wear rate limit, and the burnup, when limited by fuel performance constraints, depends on the power.

12 Sliding Wear W sliding, new W sliding, ref = y rms 1 D 2 4 I cl (D f 1 ) + new A cl ( D y rms f 1 ) + ref T c, ref ref (3.44) 1 D 2 T c, new 4I cl A cl new where A cl is cladding cross-sectional area, I cl is cladding moment of inertia, D is cladding outside diameter 12

13 P/D vs H/HM for Square and Hexagonal arrays of UZrH 1.6 and UO P/D H/HM Hydride Hex Hydride Square Oxide Hex Oxide Square 13

14 Maximum Achievable Power for Square Arrays of UO 2 at 29 psia Note: The following figures, slides 14-19, came from the paper, E. Greenspan et al, Optimization of UO 2 Fueled PWR Core Design, Proceedings of ICAPP 05, Seoul, Korea, May 15-19, 2005, Paper

15 Maximum Achievable Power for Square Arrays of UO 2 at 60 psia 15

16 Maximum Achievable Power at 29 psia Accounting for Fuel Rod Vibration and Wear 16

17 Maximum Achievable Power at 60 psia Accounting for Fuel Rod Vibration and Wear 17

18 18 Maximum Permissible Cycle Length. 29 psia

19 19 Maximum Permissible Cycle Length. 60 psia

20 Illustration of Porosity in a Wire-Wrapped Bundle 20

21 21 THV-Induced Wear Data with Otsubo s Wear Constraint where P i is the pitch, P is the porosity, d w is the wire diameter, R is the number of rings in the bundle, ΔT is the temperature drop across the bundle in C, H is the axial pitch, and L is the length of the assembly. The region above this line (labeled wear mark region) is the region where Otsubo s constraint predicts that wear will occur. In the region below the dotted line, Otsubo s constraint predicts that no significant wear will occur. The points marked with a represent reactors in which no wear has been observed, while the points marked with a * represent reactors in which wear marks occurred. The horizontal lines identify the range over which the subject fuel tests were conducted. The red dots,, used for BN-350, BN-600, and BOR-60, represent Russian fast reactor data not used by Otsubo.

22 BWR Core Design 22

23 GE9_9 Fuel Bundle 23

24 Thermal-Hydraulic Constraints 24

25 25 The Hench-Gillis correlation has the general form: AZ x = (2 J )+ F C P B + Z

26 Pin-by-Pin Power-to-Average Power Ratio at BOL for a BWR GE 9_9 Single Bundle Without Gadolinia 26

27 J1 Factors 27

28 Bundle Loss Coefficients 28

29 Coefficients for Frictional Pressure Drop Correlations 29

30 Vibration Ratio Dependence on Quality and Mass Flux, Païdoussis Correlation Source: Ferroni, P., and N. E. Todreas. "Thermal Hydraulic Analysis of Hydride Fueled BWRs" MIT-NFC-TR-079. Cambridge, MA: MIT CANES, February Courtesy of MIT CANES. Used with permission. 30

31 Païdoussis Correlation Quinn s Data Comparison 31

32 Païdoussis - Tsukuda Vibration Ratio Comparison (Restricted G Range) 32

33 Final Vibration Ratio Comparison 33

34 Locations of the Assembly Configurations Examined for / Ratio Investigation 34

35 Comparison between Relative Maximum Power and Overall Maximum Power 35

36 36 Power distribution assumptions The non-uniform radial power distribution is accounted for by means of four radial peaking factors, which reflect typical average BWR values Hot assembly: 1.45 Mid-hot assemblies: 1.3 Mid-cold assemblies: 1.0 Cold assemblies: 0.6

37 37 3 core types are considered*: 1) Oxide Backfit Core: existing BWR 5 vessel fueled with UO 2 (core radius = 3.2 m). Cruciform CRs, WRs, constant fuel channel size. 2) Hydride Backfit Core: existing BWR5 vessel fueled with UZrH 1.6 (core radius = 3.2 m). Variable fuel channel size. 3) Hydride New Core: ESBWR vessel fueled with UZrH 1.6 (core radius = 3.55 m). Variable fuel channel size. * Each core type has been modeled 400 times, i.e. each time with a different assembly configuration.

38 38 Core structural changes resulting from the implementation of UZrH 1.6

39 The greater design freedom for the hydride cores is limited by the application of 2 Structural Constraints: Hydride Backfit Core Structural Constraints Maximum Number of Assemblies* 1.6N ref (1222) Maximum Assembly Weight** 1.4M ref (361kg) Hydride New Core 1.6N ref (1222) Not Applied * to limit the refueling time. ** due to the limited load capacity of the crane in an existing plant. Not applied to the Hydride New Core since a reactor designed specifically to utilize UZrH 1.6 is assumed to be provided with a crane of sufficient load capacity. 39

40 Oxide Core Powermap 40

41 Power, LHGR and Number of Rods Ratios Between the Examined Oxide Core Configuration and the Reference Core (the lines represent unity ratios) 41

42 Whole Core Flow Rate (Oxide Core) 42

43 43 Some observations about the powermaps: What are the limiting parameters and where do they apply d MCPR (most limiting constraint) Fuel avg T The size of this area increases significantly (especially for Hydride fuel) if the fuel-clad gap is modeled as a He-filled gap*. However, for all the three core types the overall max power is not affected by the choice of the gap filling. Very tight lattice assemblies. Core _p Vibration Ratio P/d Small d rods: significantly more subject to vibrations. NOTE: Fuel Centerline T, Clad Surface T and Decay Ratio are never limiting. * Through the whole analysis, the fuel-clad gap is assumed to be filled by a liquid-metal eutectic.

44 Limiting Effect Exerted by Constraints (Oxide Core) 44

45 Core Average Exit Quality and Hot Bundle Exit Quality (Oxide Core) 45

46 Bypass Flow Percentage (Oxide Core) 46

47 Oxide Core Fuel Matrix (n_n) Size (the colored scale indicates the matrix index n; black upper line: n=7, black lower line: n=12; green line: high power region) 47

48 48 1) Oxide Backfit Core 2) Hydride Backfit Core Oxide Backfit Hydride Backfit Although the core size is the same, the Hydride Core delivers 10-25% more power! (depending on the assembly configuration considered)

49 Power, LHGR and Rod Ratios Between Hydride Backfit Core and Oxide Ref. Core (continuous lines represent unity ratios) 49

50 Limiting Effect Exerted by Constraints (Hydride Backfit Core) 50

51 51 3) Hydride New Core The benefits derived from the implementation of Hydride fuel are coupled with those (predictable) resulting from having a larger core size (ESBWR core size). For the sake of comparison, the ESBWR fueled with oxide delivers about 4500 MW th